1. Field of the Invention
The invention relates to a cosmetic product that can stably store ascorbic acid and then deliver same to the skin.
2. The Related Art
Ascorbic acid, also known by its common name of Vitamin C, has long been recognized as an active substance benefiting skin appearance. Vitamin C reportedly increases the production of collagen in human skin tissue. Wrinkles and fine lines are thereby reduced. An overall healthier and younger-looking appearance results. Vitamin C has also found utility as an ultraviolet ray blocking or absorbing agent. Whitening or bleaching skin compositions have also employed Vitamin C utilizing its property of interference with the melanin formation process. There also is a belief that ascorbic acid interacts with the human immune system to reduce sensitivity to skin-aggravating chemicals. Reduced levels of Vitamin C concentration on the skin have also been implicated with an increase in stress. From all of the foregoing perspectives, Vitamin C or ascorbic acid may provide significant benefit when topically applied.
Unfortunately, Vitamin C is a very unstable substance. Although it is readily soluble in water, rapid oxidation occurs in aqueous media. Solubility of ascorbic acid has been reported to be relatively poor in nonaqueous media, thereby preventing an anhydrous system from achieving any significant level of active concentration.
The art has sought to overcome the problem in a variety of ways. One approach is the preparation of ascorbic acid derivatives. These derivatives have greater stability than the parent compound and, through biotransformation or chemical hydrolysis, can at the point of use be converted to the parent acid. For instance, U.S. Pat. No. 5,137,723 (Yamamoto et al) and U.S. Pat. No. 5,078,989 (Ando et al) provide glycosylate and ester derivatives, respectively.
U.S. Pat. No. 4,818,521 (Tamabuchi) describes under the background technology a so-called two-pack type cosmetic wherein Vitamin C powder and other ingredients are separately packaged in different containers with mixing just prior to use of the cosmetic. The mixing procedure and expensive packaging were said to be drawbacks of this system. The patent suggests stable oil-in-water type emulsions that are weakly acidic and wherein ascorbic acid has been premixed with a stabilizing oil.
Maintenance of pH below about 3.5 has also been suggested in U.S. Pat. No. 5,140,043 (Darr et al) as a stabilization means for aqueous compositions of ascorbic acid.
Water compatible alcohols such as propylene glycol, polypropylene glycol and glycerol have been suggested as co-carriers alongside water to improve stability. An illustration of this approach can be found in U.S. Pat. No. 4,983,382 (Wilmott and Znaiden). Therein a blend of water and water-miscible organic solvent are combined as a stabilizing system. At least about 40% of the organic solvent must be ethanol while the remainder may be selected from such alcohols as propylene glycol, glycerin, dipropylene glycol and polypropylene glycol.
U.S. Pat. No. 4,372,874 (Modrovich) has reported incorporation of relatively large amounts of ascorbic acid in a polar water-miscible organic solvent such as dimethyl sulfoxide. Levels of water are kept below 0.5% through addition of a particulate desiccant to the carrier. Although highly polar systems such as dimethyl sulfoxide may be effective, this and related carriers are toxicologically questionable.
Accordingly, it is an object of the present invention to provide a delivery system for ascorbic acid in which the compound is storage stable.
Another object of the present invention is to provide a delivery system which delivers ascorbic acid at a pH compatible with that of human skin to avoid irritation and obtain better penetration.
Still another object of the present invention is to provide a system for delivering ascorbic acid that is sufficiently transparent so as to render the system aesthetically pleasing.
A still further object of the present invention is to provide a system for delivering ascorbic acid to the skin that includes a carrier which is at least half water.
These and other objects of the present invention will become more readily apparent through the following summary, detailed discussion and Examples.